1. Field of the Invention
Example embodiments relate to an electrochromic device using polyphthalate as an electrochromic material and a process for preparing the same. More specifically, example embodiments relate to an electrochromic device comprising electrodes, an electrochromic layer and an electrolyte layer, wherein the electrochromic layer includes polyphthalate, and a process for preparing the same.
2. Description of the Related Art
Electrochromism is the phenomenon displayed by some chemical species of reversibly changing color when a voltage is applied. A material capable of undergoing reversible changes of optical properties by the electrochemical redox reaction accompanying such electrochromic properties is called an electrochromic material. That is, the electrochromic material does not have a color when no electric field is applied from an external source and then has a certain color when the electric field is applied, and vice versa. Examples of the electrochromic materials may include inorganic compounds such as tungsten oxides, molybdenum oxides, and the like, and organic compounds such as pyridines, aminoquinones, and the like.
Thus, electrochromic devices taking advantage of such an electrochromic phenomenon have various advantages such as high reflectivity without a need for an external light source, excellent flexibility and portability, and the feasibility of weight reduction, and are therefore expected to have promising applications for various flat-panel displays (FPDs). In particular, the electrochromic polymer materials are receiving a great deal of attention, due to high applicability to E-paper which is recently under intensive research and study, as an electronic medium capable of replacing paper.
As the electrochromic material, an inorganic compound or an organic compound is usually employed. Specific examples of the inorganic compound may include tungsten oxides, molybdenum oxides, iridium oxides, Prussian blue, and the like. Specific examples of the organic compound may include rare-earth compounds, phthalocyanine, ruthenium complex, viologen, and the like. In particular, WO 97/035227 discloses electrochromic devices using viologen as an organic electrochromic material, wherein application of an electric field between both electrodes of the electrochromic device results in color changes of viologen molecules via the reaction of the viologen molecules with ions or electrons in an electrolyte.
That is, viologen electrochromism is dependent upon oxidation-reduction (redox) reactions. Upon transfer of electrons to viologen molecules from the electrolyte, the viologen undergoes one-electron reduction to provide a colored radical cation yielding a blue color, which will emit a yellow color upon further accepting of electrons from an electron donor.
The electrochromic device disclosed in WO 97/035227 is known to have a fast electrochromic response speed and a high contrast ratio, and an excellent bistability which is a memory property capable of maintaining an electrochromic property even after a power source applied to an electrochromic material is off. However, even though blue and green electrochromic materials are known in such a nano-electrochromic type, red electrochromic materials are not yet known.
Meanwhile, Chiba University (J. Mater. Chem., 2004, 14, 2366-2368, Chiba University/Hitachi Chemical Co., Ltd.) discloses an electrochromic device utilizing dimethyl terephthalate as an electrochromic material. However, this type of the electrochromic device suffers from no bistability, resulting from rapid electrical neutralization of the electrochromic material when a power source is off, due to use of a solution type of an electrochromic material in which the electrochromic material is dissolved in an electrolyte solution.